Testing of biological samples is often carried out using, for example, wet chemistry, in conjunction with automatic testing machines. In some such tests, samples are dispensed in reaction trays having a plurality of wells for handling a plurality of samples, with the analysis of the different samples often involving counting photons emitted from the samples. There is no known single photon counting standard, however, and, therefore, it is only possible to obtain relative relationships between single photon sources and photon detectors (photon counters).
Further, there is an intrinsic variability among photomultiplier tubes used to count photons, which variability requires a normalization method to obtain similar count values among different photon counters, such as are typically encountered in testing machines (a plurality of photon counters facilitates higher volume testing). In such cases, for example with the ABBOTT PRISM™ System available from Abbott Laboratories, Inc. of 100 Abbott Park Road, Abbott Park, Ill. 60064, the testing machine may have a plurality of different tracks for different types of tests, with each track having two photon counters, which are used in conjunction with trays having a plurality of rows of wells, with each row having two wells (e.g., two columns of wells in eight rows). In use, a tray is advanced through the testing machine row by row, with one photon counter counting photons emitted from each well of one column of wells and the second photon counter counting photons emitted from each well of the other (adjacent) column of wells.
Given the intrinsic variability and extremely sensitive nature of photon counters, however, it is essentially impossible to expect that each of the photon counters will be identical, or will obtain identical results even under identical conditions (which can never be achieved in any event). Therefore, it has been necessary to normalize the readings obtained by different photon counters, that is, to determine a factor of difference between the photon counters, which may be used to obtain comparable results among a plurality of photon counters. For example, in a simplified example, if a known source is read, and one photon counter is found to return readings that are 10% higher than the known source, and the other photon counter is found to return readings that match what would be expected from the known source, readings taken during testing by the former photon counter would be reduced to take into account the 10% overcount, thereby giving test results that are therefore more reliable. Of course, accurate test results are particularly critical in many such biological testing situations, because incorrect results are not merely testing failures, but may also result in a misdiagnosis of an individual's condition and subsequent improper treatment of a patient.
In order to determine normalization values among photon counters of a testing machine, optic module verification tools (OMVT) have heretofore been used. Such devices are essentially duplicates of reaction trays, including at least one well in each column (i.e., associated with each photon counter) having a known photon emitter.
The well of a tray 10 including such a prior art photon emitter in one of the wells of the tray is illustrated in FIG. 1. Specifically, the photon emitter 20 is disposed beneath a tray well 22, and includes an optic standard 26 contained within a capsule 28, both of which rest on a cap 30. Suitably secured over the optic standard 26 is a filter glass 34, and a foam support 36 is provided at the bottom of the tray 22 to assist in locating the filter glass 34 at the desired position adjacent the bottom of the tray well 22. The optic standard 26 is carbon-14 (C14) mixed with a suitable epoxy resin as a soup or slurry, which is then cast in the desired plug shape.
For normalization, the photon emission of each photon emitter is first measured according to a standard. For example, normalization trays have been measured at a central location where such standardized measurements can take place, with each photon emitter assigned the measured photon count. Such normalization trays have then been distributed for use with testing machines, with one normalization tray provided at each geographic location where a testing machine is found.
At each testing machine, the normalization tray is run through the machine one or more times in order to obtain a photon count by each photon counter from the photon emitter associated therewith. The photons counted at the test machine by each photon counter are then been compared to the assigned measured photon count as previously determined for each photon emitter, with those values used to normalize the results obtained by the different photon counters, when photons emitted from test specimens are subsequently counted.
Unfortunately, while the photon emitter such as described above might be thought to be subject to little decay, because it is based on C14 having a long half-life (5568 years), experience has shown that the photons emitted by such emitters in fact may decay relatively quickly, so that the quantity of emitted photons may fall below a desired minimum level in as short a period of time as a few months. In that case, a new optic module verification device (normalization tray) can be obtained from the central location (or the old one must be essentially completely remanufactured with a new photon emitter) with normalization values obtained against the standard. Alternatively, the device can continue to be used after being re-measured according to the standard, but with photon emissions that are below the preferred minimum level for reliable normalization of the test machine. Neither option is preferred for both cost and operational reasons.
The present invention is directed toward overcoming one or more of the problems set forth above.